Technical Abstract:
The model legume Medicago truncatula provides an excellent tool to study growth and development in a symbiotic system. With the sequencing of the M. truncatula genome in progress and work being undertaken to create single-gene mutants, in the near future we will have essential resources to evaluate the effects of genetic lesions on many growth processes. It is imperative that we have a detailed baseline understanding of the growth and developmental pattern associated with one of the most commonly used wild-type M. truncatula, line A17 of cv. Jemalong. Such information in combination with gene expression profiling will be essential in the characterization of gene function as it relates to legume biology. We have initiated studies that characterize the morphological development of M. truncatula A17. Specifically, our objectives are: (1) to define key growth-stage landmarks where morphological characteristics can be clearly identified; (2) to outline the temporal developmental pattern; and (3) to develop a uniform decimal code that identifies specific stages in the overall development of the shoot and root. The identification of key growth-stage markers will be important in describing morphological mutants of interest altered at a specific stage of development. Establishing an outline of the temporal developmental pattern will assist in the characterization of mutants having a subtle or a developmentally impaired phenotype. The creation of a uniform code identifying specific stages in development will initiate a universal nomenclature system for phenotypic scoring that may be used and understood by the entire M. truncatula community. We have determined the growth and developmental patterns of M. truncatula A17 from germinated seed to early pod formation. Thereby, identifying the sequential steps associated with M. truncatula shoot and root growth over this period. This information has been used to identify specific phenotypic alterations as they relate to the temporal and morphological changes associated with plant growth under nutrient stress. We are in the process of testing this system to analyze, characterize, and differentiate various M. truncatula ecotypes. Our goal is to create a framework for the future analysis of phenotypic alterations of M. truncatula due to either genetic mutations or environmental conditions.